1. Field of the Invention
The present invention relates to a semiconductor wafer marking system, and more particularly, to a semiconductor wafer marking apparatus having a marking interlock system and a semiconductor wafer marking method using the same.
2. Description of the Related Art
In general, photography, ion diffusion, etching, and deposition are repeatedly performed on a wafer when manufacturing a semiconductor device. A test process is then performed on the wafer following manufacturing of the semiconductor device to determine whether the wafer has defects. When the test process is completed, the wafer is cut in a scribing process, and is packaged to form chips.
An identification mark is provided on a portion of the wafer to identify the wafer in the semiconductor manufacturing process. The identification mark is provided to manage various and strict process conditions for respective semiconductor manufacturing processes, or to indicate a product name, management code, manufacturing date, etc. The identification mark is marked using numerals, characters, or symbols composed of dots on a portion of the surface of a wafer.
Marking methods for forming an identification mark on a semiconductor wafer can generally be classified as ink marking methods and laser marking methods. The laser marking method is preferred because of its convenience and easy maintenance. In a typical laser marking method, a continuous pulse-type laser is radiated on a portion of the surface of a semiconductor wafer using an optical system such that dot shape characters or numerals are marked on the semiconductor wafer. As semiconductor devices continue to become more highly integrated, several hundred process steps may be required to manufacture a semiconductor device. Accordingly, to obtain the history of the manufacturing processes, instead of a simple identification mark, mark history data of the manufacturing processes is made on a wafer. In general, a laser, for example, a He—Ne laser, is radiated on a wafer on which an identification mark is marked and then the identification mark is read using changes in a reflection ratio or thermo-wave vibration of the laser reflected from the wafer. The process conditions for manufacturing a semiconductor device are defined according to the data read.
Referring to FIG. 1, a conventional laser marking apparatus radiates a laser beam generated from a laser head unit (not illustrated) onto a wafer 10 through an optical system to form an identification mark 20 on a predetermined region of the wafer 10. The identification mark 20 includes characters or numerals composed of dots. In a wafer marking method using the conventional laser marking apparatus, when laser energy generated by a laser diode is too weak, dots are not sufficiently formed on the wafer 10. If processes of manufacturing semiconductor device are performed, a portion of the identification mark, e.g., the portion enclosed within the solid circle of FIG. 2A, is concealed by chemicals during the manufacturing processes such that the identification mark 20 becomes useless.
If the laser energy is too strong, particles 22 are generated as illustrated in FIG. 2B. The particles 22 are adsorbed onto device forming regions 11 of the wafer 10 which can cause defects in the semiconductor devices of the device forming regions 11. In addition, the particles adsorbed onto the device forming regions 11 can scratch the surface of the wafer during subsequent processes, for example, during a chemical mechanical polishing (CMP) process. Such a marking defect cannot be detected during the marking process, but only after the subsequent manufacturing processes have been completed. For this reason, the conventional method is disadvantageous in terms of costs and time.
FIG. 3 is a perspective view of a laser head unit of a conventional semiconductor wafer marking apparatus 30. Referring to FIG. 3, the conventional semiconductor wafer marking apparatus 30 includes a laser source 60 and a flowcell 40. The laser source 60 includes laser diodes and generates a laser to form the identification mark 20 on the wafer 10. The flowcell 40 disperses the laser radiated from the laser source 60. The flowcell 40 is fixed on a table 50, and the laser source 60 is disposed above a laser radiation region 41 of the flowcell 40.
A pipe 90 through which cooling water flows is disposed inside of the flowcell 40 and is connected to a cooling water reservoir 70 where the cooling water is stored. Accordingly, the temperature of the laser radiation region 41 of the flowcell 40 can be maintained at a constant level due to the presence of the cooling water supplied from the cooling water reservoir 70. When the cooling water flowing through the pipe 90 maintains the flowcell 40 at a constant temperature, the flowcell 40 disperses the laser energy which is emitted by the laser source 60. The laser dispersed by the flowcell 40 is transmitted through an optical system (not illustrated) on the wafer 10 as illustrated in FIG. 1, and forms the dot type identification mark 20.
In the conventional semiconductor wafer marking apparatus 30, the energy of the laser beam radiated onto the wafer 10 should be constant so as to precisely mark the identification mark 20 on the wafer 10. If the energy of the laser beam radiated onto the wafer 10 varies, dot defects or particles are generated, as described above. A common cause of the change in the energy of the laser beam radiated onto the wafer 10 is the temperature of the laser radiation region 41 of the flowcell 40. The temperature of the laser radiation region 41 is dependent on the temperature of the cooling water stored in the cooling water reservoir 70 and circulated in the flowcell 40 through the pipe 90. Because the cooling water circulated in the flowcell 40 maintains the laser radiation region 41 at a constant temperature, when the temperature of the cooling water is changed, the temperature of the laser radiation region 41 of the flowcell 40 is also changed. Due to such a temperature change, the dispersion of the laser radiated onto the laser radiation region 41 is changed, thereby changing the energy of the laser beam radiated onto the wafer 10 through the optical system.
In the conventional marking apparatus, a temperature sensor 71 is attached to the cooling water reservoir 70 and controlled by a controller 80 to maintain the cooling water stored in the cooling water reservoir 70 at a constant temperature. However, only the temperature of the cooling water in the cooling water reservoir 70 is maintained at a constant level, and not the temperature of the cooling water circulating in the flowcell 40 through the pipe 90. Accordingly, even through the temperature of the cooling water in the cooling water reservoir 70 is maintained at a constant level, the temperature of the cooling water circulated through the pipe 90 in the flowcell 40 can be changed such that the temperature of the laser radiation region 41 of the flowcell 40 is changed, resulting in variation in the energy of the laser beam used for the wafer marking.
Another potential cause of change in the energy of the laser beam is cooling water leakage in the pipe 90. The cooling water leakage in the pipe 90 changes the temperature of the cooling water and the energy of the laser beam. Another potential cause of change in the energy of the laser is the input current signal that is input to the laser diode of the laser source 60. That is, the input current changes the energy of the laser generated by the laser diode, thereby changing the energy beam radiated onto the wafer 10.
In the conventional marking apparatus, there is no unit which can detect the cooling water leakage in the pipe 90 in the flowcell 40 or the level of the input current supplied to the laser diode of the laser source 60. Therefore, a marking operation is performed even when a cooling water leakage occurs or when a change in the input current supplied to the laser diode is generated during the wafer marking operation. Consequently, the above-described marking defects cannot be prevented.